2.1 The type of needle guard to which this invention relates has been described in Patent Cooperation Treaty application No. PCT/CA90/00031 published on Aug. 9, 1990 under international publication number WO 90/08564.
2.2 This cited prior application describes a range of configurations for needle guard devices which are stored at the base of a needle and which automatically engage with and cover the tip of a needle when moved to the tip.
2.3 Two references which do provide self-deploying needle guards on an intravenous catheter are:
(1) European patent application No. 89306957.5 of Lemieux published 31 Jan., 1990 as No. 0 352 928; and PA1 (2) PCT application PCT/US 90/03987 of McLees published on 7 Feb., 1991 as WO 91/01151. PA1 (1) European patent application No. 89306957.5 of Lemieux published 31 Jan., 1990 as No. 0 352 928; and PA1 (2) PCT application PCT/US 90/03987 of McLees published on 7 Feb., 1991 as WO 92/01151. PA1 3.2.1 A body having an axial needle passageway extending the length of the body, and also having other laterally-accessible component cavities. PA1 3.2.2 A canting lever with a locking plate at its one end and a sensing plate at its other, installed in one of the above component cavities. PA1 3.2.3 A spring, mounted in one of the above component cavities, and arranged to hold the sensing end of the lever in contact with the side of the insertion needle shaft. PA1 3.2.4 A shell of one or more pieces, enclosing the body and its contained lever and spring. PA1 3.2.5 The shell of the present invention will be described herein as comprising an inner shell and a partially surrounding outer shell, with the outer shell being generally the more distal of the two.
Neither of these applications permit utilization of a standard, featureless cylindrical needle.
2.4 One embodiment in the cited prior PCT patent application PCT/CA 90/00031 relates to the installation of the needle guard on an intravenous catheter assembly, in which the needle guard is frictionally retained on the base or hub of the catheter, until the needle guard locks over the tip of the insertion needle, as the latter is withdrawn from the catheter. Continued needle withdrawal motion is then transmitted to the locked needle guard, and additional withdrawal force overcomes the frictional grip of the needle guard on the catheter hub, allowing the needle guard to separate from the hub for disposal with the needle.
2.5 This embodiment requires that the user of the intravenous assembly hold the catheter hub with hand A while withdrawing the needle by pulling on its base with hand B. It thus requires no change in the user's accustomed manipulative procedure used with an ordinary catheter assembly.
2.6 However, if the user withdraws the needle by using hand B grip and pull the needle guard instead of the needle base, the needle guard will separate prematurely from the catheter while the needle point is still outside the body of the needle guard, and therefore unprotected. This malfunction defeats the purpose of the needle guard.
2.7. The above embodiment further requires that the withdrawal force required to overcome the frictional grip on the catheter hub of the locked needle guard be significantly greater than the frictional drag between the needle and the needle guard when the latter is being slid along the needle shaft during the withdrawal motion. This is to ensure that the needle guard does not separate from the catheter hub before the needle guard locks over the needle tip. However, this frictional separation force must not be excessive, as it may cause the catheter to be jerked involuntarily toward and into the patient by the user's hand A at the moment of separation, causing possible injury. These conflicting frictional requirements place significant constraints on the design of the needle guard assembly.
2.8 The invention described herein relates to a further embodiment of the above prior applications whereby the needle guard is retained on the catheter hub by a positive engagement means between the needle guard and the hub, instead of by friction. This engagement means is released only after the needle guard has locked over the needle tip, allowing the needle guard to separate from the catheter hub without significant further withdrawal effort.
2.9 With this embodiment, if the user's hand B accidentally grips the needle guard instead of the needle base during withdrawal, the user will be unable to separate the needle guard from the catheter hub, and must transfer the grip of hand B correctly to the needle base before he can withdraw the needle.
2.10 Furthermore, if hand A should accidentally grip the needle guard instead of the catheter in order to restrain the catheter during withdrawal of the needle, the needle will draw out and the needle guard will lock in the normal way. This will release the needle guard to separate from the catheter hub with little or no further pulling effort. It is therefore immaterial whether the catheter is restrained with hand A by holding its hub, or by holding the needle guard.
2.11 With this embodiment, the needle guard must lock to the needle shaft, covering the needle tip, before the needle guard can be released from its positive engagement with the catheter hub. Thus the needle tip cannot be exposed under any circumstances, following attachment of the needle guard and needle to the catheter hub.
2.12 Two references which do provide self-deploying needle guards on an intravenous catheter are:
Neither of these applications permit utilization of a standard, featureless cylindrical needle.